(a) Field of the Invention
This application relates to a multiple system and methods for controlling the flow and residence time of gases and emissions through an exhaust flue. More particularly, but not by way of limitation, to an adjustable co-axial flue flow adjustment system.
(b) Discussion of Known Art
It is well recognized that adjusting the residence time of the exhaust gases moving along the flue can optimize the efficiency of devices such as furnaces. Optimized combustion results in reduced harmful emissions, such as carbon monoxide, shorter on cycles, longer off cycles and reduction in the amount of fuel and electricity consumed. However, the problem of how to achieve this optimization has proven difficult to solve due to the unpredictable nature of fluid flows and to limitations imposed by regulatory authorities.
As to regulatory limitations, flue ducting may not be restrictive in any location. This means that the cross-sectional area of the flue may not be reduced anywhere along the flue. Thus, the problem of how to increase residence time of the exhaust gases while reducing emissions traveling along the flue, without introducing restrictions to the flow.
Some known examples include U.S. Pat. No. 4,836,184 to Senne and U.S. Pat. No. 4,499,891 to Seppamaki provide baffles that extend into the flow, and thus disturb the laminar flow in order to create turbulence and increase the residence time of the flow within the flue. The tuning of these known devices is carried out by simply increasing or decreasing the extension of the baffle in order to increase or decrease the projected area of the baffle as seen by the flow.
Other known devices include U.S. Pat. No. 5,666,942 to Kazen and U.S. Pat. No. 5,411,013 to Kazen. The approaches in these devices was to increase residence time by placing a spiral ribbon in a section of flue duct, and thus force the flow to follow the ribbon in order to increase the residence time of the exhaust gases in the flue. Kazen's devices, along with other known prior art, because they were installed directly within the exhaust system and not within an expansion system, are restrictive by design and prohibited under regulatory guidelines.
Problems associated with known devices include that due to the fact they work well in only certain boiler systems, and not in forced air systems, and visa-versa. For instance the device to Senne was relatively simple to install in industrial boilers, but difficult to install in home applications, where forced air systems are more predominant. Senne's applications for boiler systems could be pre-calculated or pre-set for providing optimal performance to a specific boiler system, but had to be tuned in the field for forced air systems. This in turn required that highly trained technicians be used for home applications. Still further, home applications are typically found in tight spaces, which can rule out the use of the Senne device.
Still further, as shown in FIG. 1, in the design of the Senne device the minimum flow area is along the plane of the plate to the top of the plate, and then in a plane to the top of the 45-degree shoulder. This presents an important drawback in that modifications to improve the minimum area are at a cost of reduced system performance; conversely, larger plate sizes for increased performance violate the nonrestrictive design requirement.
Accordingly, the specific requirements for the configuration for application to both home and industry are:
1. Comply with the accepted standard that all exhaust ductwork not be restrictive in any location. This translates to the statement that the minimum flow area in the device be greater than the inlet duct area, Amin/Ainlet≧1.0;
2. Do not reduce the draft by 50%, stay in the range of 20 to 30%.
3. Maintain furnace temperatures Tfurnace≦250° F.
4. For home use provide a fixed position of the deflector plate inside the disclosed invention in order to use as is, and also to provide a safety measure which prevents untrained installers from altering the device. For industrial use, provide capability for adjustable vernier settings.
5. Reduce the footprint in recognition of the tight spacing of the home exhaust duct network.
6. Installation of the disclosed invention shall be no closer than 1 foot from the exit of the gas fired appliance.
7. Construction is made of stainless steel in order to combat corrosion.
8. Absolutely no leakage.
9. Absolutely nothing can come loose and fall down the flue.
10. Maintain open area without screens/porous baffles, which can clog with soot.
11. Use standard size ducts and connections for ease of installation.
12. Design and manufacture the product so that no retrofitting to the gas fired appliance is required at the time of installation
13. Provide capability for both draft hood systems and induction fan systems.
The last requirement implies a wide range of capability of the configuration. This will necessarily force two examples that include the inventive aspects disclosed here, since the two systems operate quite differently. The two applications will be addressed in the system performance section.